Fixes #15120

Change-Id: I1d9a192ac163826bad8b46e8c0b0b9e218e69570
Reviewed-on: https://go-review.googlesource.com/21520Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/21698
Run-TryBot: Andrew Gerrand <adg@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>